Foams are dispersions in which a gas is dispersed in a liquid material, a solid material, or a gel material. Solid foams include closed-cell foams and open-cell foams.
In closed-cell foam, the gas forms discrete pockets, where the discrete pockets are completely surrounded by the solid material. The closed cells may be referred to as non-intercommunicating. Because the discrete pockets are completely surrounded by the solid material, the closed cells form a rigid material, e.g., a rigid foam. Additionally, the closed cells help to prevent passage of gases or liquids through the closed-cell foam. Closed-cell foams are used in a variety of applications, such as thermal insulation, vapor insulation, liquid insulation, joint filling application, and impact protection applications, among others.
In contrast to closed-cell foam, in an open-cell foam the gas pockets connect with each other. The open cells may be referred to as intercommunicating. Because the gas pockets of an open-cell foam are not completely surrounded by the solid material, the open cells can form a flexible material, e.g., a flexible foam or a viscoelastic foam. Open-cell foams are used in a variety of applications, such as some insulation application, packaging applications, automotive trim, filters, and acoustic applications, among others.